1. Field of the Invention
The present invention relates to a vehicle perimeter monitor carried by a vehicle for watching vehicle perimeter and more particularly to a vehicle perimeter monitor which calls attention to the driver in order to avoid contact or collision with obstacles such as other vehicles during traffic lane change.
2. Background Art
As a conventional vehicle perimeter monitor, for example, Japanese Patent Laid-Open No. 325688/1999 discloses a vehicle perimeter monitor which comprises a transmitting circuit for generating transmit wave, an antenna carried around or interior of a door mirror apparatus of a vehicle for radiating transmit wave by way of the door mirror and a receive circuit which receives reflected wave from back by obstacles existing in the perimeter of vehicle with the aid of a receiving antenna by way of mirror surface of the door mirror apparatus. Furthermore, this conventional example is characterized in that on the mirror surface of the door mirror apparatus is deposited reflective coating which allows electromagnetic waves of several GHz-100 GHz to pass through though reflecting back waves having a wavelength of visible light.
In such a conventional monitor, the reflective coating which allows electromagnetic wave to pass through is deposited on the door mirror but there also exists reflections in some degree by the surface of mirror base material and the reflective coating. Furthermore, in case that the antenna is carried interior of the door mirror, the positional relationship between the door mirror and the antenna fluctuates every time when the viewing direction of the door mirror attached to the outer casing of the door mirror apparatus is adjusted by an actuator resulting in that the reflection of transmit wave caused by the door mirror is not maintained constant. Consequently, the condition seems as if an obstacle always exists within a very short distance and so in case that an obstacle exists within a very short distance in reality, there arises a problem that the obstacle can not be detected depending on the range resolution of the radar or that the possibility of false alarm is enhanced because of the deterioration of the range-finding performance of a short distance.
The present invention has been made to resolve such problems as described above and an object of the present invention is to provide a vehicle perimeter monitor having a superior range-finding performance of a short distance and capable of providing a correct information to a driver.
The vehicle perimeter monitor according to the invention is one carried by a vehicle having a door mirror consisting of the material which allows radio wave to pass sufficiently, a support member for supporting the door mirror and an actuator for moving the door mirror with the support member integrally to change viewing direction, the monitor comprising a transmitting antenna fixed on the support member for radiating transmit wave generated by a transmitting circuit to the perimeter of the vehicle through the door mirror, a receiving antenna fixed on the support member for receiving the reflected wave reflected obstacles existing in the perimeter of the vehicle through the door mirror to send a receiving information to a receiving circuit, a processing unit for calculating the distance between the vehicle and the obstacles based on the receiving information and determining danger degree of collision and a indicator for notifying the result of calculating by said processing unit to the driver of the vehicle.
According to the vehicle perimeter monitor of the invention, because the transmitting antenna and the receiving antenna are fixed to the support member for supporting the door mirror, the positions of the transmitting antenna relative to and the receiving antenna or the door mirror are always kept constant even if the driver changed the viewing direction of the door mirror. Therefore, as the reflection of transmit wave from the transmitting antenna is measured beforehand to be canceled, the range-finding performance of a short distance is improved and it is made possible to get rid of false alarms.
In addition, the transmitting antenna is installed at such a distance from the door mirror that the reflection of the transmit wave by the door mirror becomes smallest.
By setting the reflection of transmit wave by the door mirror smallest, the influence of reflection caused by the door mirror is restrained and so the range-finding performance of a short distance is improved furthermore.
Additionally, the transmitting antenna has a radiation pattern shaped to cover a wide area so as to be capable of covering required detection area even in the case that the driver changed the viewing direction.
By setting the reflection of transmit wave by the door mirror smallest, the influence of reflection caused by the door mirror is restrained and so the range-finding performance of a short distance is improved furthermore.
Furthermore, the transmitting antenna and the receiving antenna is attached to support members respectively by means of holder members having different shapes to each other at left and right door mirror apparatus.
By attaching the transmitting antenna and the receiving antenna to left and right door mirror respectively by use of holder members having different shape to each other, the transmitting antenna and the receiving antenna can be deployed interior of the door mirror even in the case that the viewing direction of the driver and the door mirror differs between left and right door mirror apparatus.